The present invention relates to a method for correcting for exposure in rendered digital images captured by a digital camera or the like, which corrected images are particularly suitable for printing.
Digital images which can be captured by scanners or digital cameras, or produced by a computing process, have to be rendered so that they can be properly viewed on a display. The resulting digital images are often referred to as being in a xe2x80x9crenderedxe2x80x9d image space, such as sRGB, where the relationship between the image code values and the scene luminance values is very non-linear, as depicted in FIG. 8. Digital images, whether obtained from scanned film or from digital cameras, often contain exposure errors, where the key subjects of the picture are lighter or darker than desired by the user, due to imperfect exposure determination algorithms in the digital camera or film scanner which created the digital image. Many imaging applications, such as Adobe Photoshop or Kodak PictureEasy, permit the user to adjust the xe2x80x9cbrightnessxe2x80x9d, xe2x80x9ccontrastxe2x80x9d, and/or xe2x80x9cgammaxe2x80x9d of the image by sliding using one or more xe2x80x9cslidersxe2x80x9d controlled by a mouse. Each control adjusts one of the slope, x-intercept, or exponential function applied to the image, typically using a look-up table, in order to modify the tone reproduction of the image when it is displayed or printed. However, because they do not directly adjust the scene exposure, they do not properly compensate for camera exposure errors. While it is possible to somewhat improve the image using such controls, it is extremely difficult for unskilled users to determine how to best set these multiple controls.
Some applications, such as Adobe Photoshop, also permit the user to modify a xe2x80x9clookup tablexe2x80x9d by inputting a curve of any arbitrary shape. However, only a skilled user is able to determine what curve shape provides the best image, and only then using a tedious trial-and-error process.
It is an object of the present invention to provide a method that properly compensates for camera exposure errors which is extremely simple for a non-expert to understand and use.
This object is achieved in a method for correcting for exposure in a digital image, comprising the steps of:
(a) providing a rendered digital image suitable for display and displaying such digital image;
(b) using an adjustable exposure setting to nonlinearly modify the rendered digital image to effect an exposure change and displaying the exposure modified rendered digital image; and
(c) iteratively changing the adjustable exposure setting in accordance with the nonlinear function to change the exposure setting and display modified digital images until a desired exposure modified rendered digital image is displayed.
It is an advantage of the present invention that exposure problems can be properly compensated with a minimum of user intervention.
Another advantage of the present invention is that it is extremely simple for a non-expert user to understand and use.
A feature of the invention is that it is particularly suitable for adjusting rendered digital images captured by an image capture device and for causing a printer to make aesthetically pleasing prints of images.